ChemCatChem最新文献

The development of photoelectrochemical (PEC) devices involves the attachment of molecular photosensitizers onto solid supports. Particularly significant to this work are PECs that rely on ruthenium-based photosensitizers on high band gap metal oxide (MOx) supports. In this study, we have explored a new ester binding motif (MOx-ester) to covalently attach a ruthenium polypyridyl photosensitizer to TiO₂. This new MOx-ester photoanode is compared to the traditional photoanodes that utilize acid/base binding groups to attach the molecular Ru sensitizers to TiO₂. The new MOx-ester binding motif is characterized by cyclic voltammetry UV-Vis, solid state ¹³C NMR, and FTIR-ATR spectroscopic analysis. The MOx-ester covalent bonding led to higher TiO₂ surface coverage compared to carboxylate binding, which is advantageous in terms of achieving higher light absorption per area. Electrochemical impedance spectroscopy (EIS) revealed that ester anchoring exhibits lower charge-transfer resistance compared to the carboxylate binding, leading to greater charge recombination. Despite the difference in charge recombination dynamics, comparable initial photocurrent densities were observed for the two types of binding groups. However, the ester binding group exhibited superior stability over time, compared to the carboxylate binding group in acetonitrile solution.

Cobalt spinel (Co₃O₄) catalysts are widely studied in scope of the electrocatalytic oxygen evolution reaction (OER), yet the role of interfacial structural transformation under anodic bias remains under debate. Here, we employ an operando approach, combining a fast electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D), electrochemical impedance spectroscopy (EIS), and Raman spectroscopy to investigate interfacial transformations of Co₃O₄ nanoparticle electrodes in alkaline electrolyte. We identify two distinct regimes during the anodic sweep prior to the macroscopic OER onset. At lower potentials, the catalyst interface remains mechanically rigid while reversibly associating several OH⁻/H₂O species per oxidized cobalt site. At higher potentials, pronounced softening of the interface occurs alongside further uptake of electrolyte species. This indicates amorphization and a ‘swelling process’ beyond simple adsorption. Notably, an electrochemical conditioning treatment can suppress mass and compliance hysteresis without affecting OER activity, suggesting that most incorporated electrolyte species do not participate in the OER. EIS further reveals that OER intermediates form well below the apparent OER onset potential. These results advance our mechanistic understanding of interfacial transformations in cobalt-based OER catalysts and establish EQCM-D as a sensitive operando technique for probing electrocatalyst transformations.

Formic acid is a promising hydrogen carrier. Herein, we synthesized and profiled a series of manganese-based complexes containing a quinoline-pyridinium amidate N,N′-bidentate coordinating ligand, MnX(CO)₃(N,N’), for catalytic formic acid dehydrogenation. The activity of these novel manganese complexes was dependent on the metal-bound halide as well as the motif of the donor-flexible pyridinium amidate ligand. The ortho′-methylated ortho-pyridinium amidate system Mn3 showed highest activity and reached up to 400 turnovers and a turnover frequency of 1100 h⁻¹. Modification of the catalytic conditions unveiled the importance of the water concentration and a direct temperature dependence, with a large activation enthalpy (ΔH^‡ = 99 kJ mol⁻¹) and a close to zero activation entropy (ΔS^‡ = –37 J K⁻¹ mol⁻¹). Mechanistic investigation further suggest that the process is homogeneous, and that the turnover-limiting step is the β–hydride elimination of formate from a catalytically active species that comprises both the halide and the PYA ligand bound to the manganese center.

The metal-support interaction (MSI) effect of different supports, namely, N-doped graphene (N-graphene) and CeO₂(111), on the properties of the planar 2D and 3D isomers of copper clusters of atomicity five was computationally studied at the PBE level (+U for Ce). For graphene-based systems, both pristine and defective sheets were considered. The stability, geometry and electronic properties of the supported Cu₅ clusters are discussed, and the dissociation of O₂ is studied on the most stable systems for both isomers. As expected, the interaction between Cu₅ and clean graphene or N-graphene is weak, and although adding nitrogen to graphene enhances the interaction, proper chemical adsorption is only achieved on the defects explored. In contrast, both Cu₅ isomers interact strongly with CeO₂(111). The weaker MSI with N-graphene materials allows the deformation of the Cu₅ cluster upon O₂ adsorption, whereas CeO₂(111) supported structures are more robust. O₂ dissociation on N-graphene-supported Cu₅ is consistent with our previous results on gas-phase clusters, i.e. the 2D isomer is more resistant to oxidation than the 3D one but the latter is more easily reducible, while on CeO₂(111) this trend is reversed due to the strong MSI.

Cyclohexanol is a key intermediate in the production of cyclohexanone, a ketone widely used in the chemical industry, especially in the manufacture of nylon and other polymers. In this work, we propose an alternative route based on the indirect electrooxidation of cyclohexanol in an organic medium, using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and different organic bases as the redox mediator. Cyclic voltammetry and in situ FTIR were used to elucidate the reaction mechanism and confirm the product identity, while controlled-potential electrolysis assessed the synthetic performance. The results indicate that electrooxidation occurs efficiently at 0.26 V (vs. Fc/Fc⁺) in the presence of 1,1,3,3-tetramethylguanidine (TMG), which showed superior alcohol transformation. Chronoamperometry revealed current decay after 120 min, associated with substrate consumption. In situ FTIR and FTIR-ATR confirmed selective cyclohexanone formation with a characteristic band at 1709 cm⁻¹. After 4 h of electrolysis, conversion reached approximately 94 ± 6% with a Faradaic efficiency of 83 ± 5%.